Wheat Seed Treatments

Douglas J. Jardine and Robert L. Bowden

Extension Plant Pathologist and USDA ARS Plant Pathologist 

  This document is also available as a PDF: WheatSeedTreatments.pdf

There are many different seed treatments available for wheat (see table). Although most seed treatment ingredients are fungicides, lindane and imidacloprid are insecticides. Each ingredient has certain strengths and weaknesses which may depend on the particular rates used. Many commercial formulations are complementary combinations of ingredients in order to provide a broader spectrum of protection. Azoxystrobin, carboxin, difenoconazole, fludioxonil, imazalil, imidacloprid, mefanoxam, metalaxyl, tebuconazole, thiabendazole, thiamethoxam, triadimenol and triticonazole are systemic, while the others are surface-acting protectants.

A major use of seed treatments is for the control of seed¬borne smuts and bunts. Loose smut control requires a systemic fungicide like carboxin, tebuconazole, difenocon¬azole or triadimenol. Common bunt can be controlled with most commercial treatments. In recent years, a disease called Karnal bunt has been detected in the southwestern U.S.A. Quarantines are established to keep Karnal bunt out of the Great Plains.

A second major use of seed treatments is to improve stand establishment. Most treatments do at least a fair job of controlling seed rots and seedling blights. Scab and black point are two seedborne diseases that can reduce seed germination. If seed has either of these, it should be cleaned to remove all light test weight seeds and then tested for germination rate. If the germination rate is low (less than 90%), a seed treatment could help increase the germination rate. Several products are available if wireworms are expected to be a problem in stand establishment.

The third use is root rot suppression. Unfortunately, none of these treatments gives high levels of control. Difenoconazole and triadimenol give some suppression of take-all root rot. Difenoconazole, tebuconazole and triticonazole are labeled to suppress Fusarium root rot (dryland foot rot). Imazalil, tebuconazole, and triadimenol give some control of common root rot. Triadimenol, tebuconazole, and imazalil can shorten the coleoptile, so avoid deep planting with these treatments.

The fourth use of seed treatments is control of fall-season foliar diseases. Tebuconazole, triadimenol, and difenoconazole provide protection against fall infections of powdery mildew, leaf rust and Stagonospora nodorum leaf blotch. However, these diseases may or may not be reduced in the following spring.
 

The last use is insect control. Lindane is the old standby for wireworms. Imidacloprid and thiamethoxam are labeled for control of wireworms and fall-season aphids. Aphids include greenbugs, Russian wheat aphids, bird cherry-oat aphids, and English grain aphids. To get good control of aphids, the highest labeled rates of these materials must be used. Imidacloprid and thiamethoxam used at the high rate have been shown to reduce incidence of barley yellow dwarf virus, which is carried by some aphids in the fall.

Sometimes seed treatment results in obvious stand improvements, but most of the time effects are difficult to detect visually. Producers must balance the possible benefits against the cost and the possibility of having leftover treated seed. Leftover treated seed can be avoided by using hopper box treatments. If seed is treated on-farm, pay close attention to thorough coverage of the seed.

For seed production fields, a systemic seed treatment is highly recommended to help keep seedborne pathogens such as bunt and loose smut out of seed stocks. In addition, seed treatments sometimes improve stands. Due to the high value of the seed produced, even small yield increases can justify the use of seed treatments.

For grain production fields, seed treatment economics are less certain. Conditions favoring use of standard seed treatments in grain production fields include: 1) high yield potential field, 2) seed saved from field with loose smut or bunt last year, 3) expensive seed, 4) low planting rates, 5) planting under poor germination conditions, especially late planting, or 6) poor quality or old seed.

It is difficult to make recommendations about the new seed treatments with activity against root rots, fall foliar diseases, fall season aphids, wireworms, or barley yellow dwarf. Pest pressure varies widely, and control is usually not complete. The novel treatments tend to be expensive and are most likely to be profitable for seed production fields and grain production fields with high yield potentials.

For more information about wheat, visit the Kansas State University Wheat Page    

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